1. Technical Field
This invention relates generally to an apparatus and method for analyzing a fluid sample, and, more particularly, to a self-contained analyzer for on-site use and analysis.
2. Discussion of the Related Art
There has been much interest and investigation into apparatus and methods for obtaining accurate analysis of lubricating oils (used and fresh) as well as functional fluids. The term xe2x80x9cfunctional fluidsxe2x80x9d relates to liquid materials used in mechanical equipment, and which may be or may perform primarily lubrication and/or power transmission functions (e.g., gearbox oils, automatic transmission fluid, machine oils and hydraulic fluids or oils, etc.). xe2x80x9cFunctional fluidsxe2x80x9d also includes coolants, thermal transmission media, and fuels. The reasons for such interest include, but are not limited to, (i) the assessment of the constituent, condition and quality of the oil/fluid, (ii) the condition of the equipment from which the oil/fluid was drawn, and (iii) the condition of components of such equipment.
As is known, oil is generally used to lubricate moving parts in mechanical systems, such as engines, transmissions, hydraulics and vehicles. Certain substances, referred to generally as contaminants, are not originally present in the oil but rather are produced as the by-products of wear and corrosion. For example, metal particulates may be formed through abrasion or chemical corrosion and cause further deterioration of internal parts. In addition, normal operation causes oxidation, nitration and sulfation of the oil, altering a desired chemistry thereof. Further, leaks between the cooling systems and the lubricating system may cause coolant (mixtures of water, ethylene glycol and other coolant chemicals) to be introduced into the oil.
Lubricant oil filters are designed to remove the larger size particulates from oil. However, this gross filtering nonetheless leaves the majority of smaller contaminants free to further affect the equipment. For example, non-metallic components, such as pump diaphragms, gaskets and seals, fluid lines and the like, may be further affected. Moreover, contaminants in the oil, such as ethylene glycol, fuel, silicone, water, soot and other chemicals may also present concerns.
Historically, accurate oil analysis has been provided mainly in a laboratory setting, such as, for example, a system utilized in a laboratory as disclosed in U.S. Pat. No. 3,526,127 issued to Sarkis on Sep. 1, 1970.
One approach to accurate on-site oil analysis was to provide a self-contained test assembly in a single housing, as described in U.S. Pat. Nos. 5,517,427 and 5,537,336, both issued to Joyce (the xe2x80x9cJoyce patentsxe2x80x9d), both hereby expressly incorporated by reference in its entirety. The Joyce patents disclose a test assembly that includes an infrared (IR) spectrometer and an optical emission spectrometer for producing a report on the amount of certain metals in an oil sample, other oil contaminants such as water, glycol, soot, etc. as well as oil condition. With respect to the optical emission spectrometer portion, the Joyce patents disclose the use of xe2x80x9cphotocellsxe2x80x9d (the commercial embodiment corresponding to the Joyce patents employed well-known photo multiplier tubes (PMT)) to optically monitor spark induced light emissions of the oil sample to determine wear metals content.
Although PMTs in the manner configured (i.e., incorporated into a large monochromator in the commercial embodiment corresponding to the Joyce patents) provide xe2x80x9chigh resolutionxe2x80x9d, such a configurations presents certain constraints. First, inherent in such systems are certain geometric and mechanical constraints imposed by the physical dimensions of a PMT. Since each PMT was configured to monitor a fixed wavelength, the system had to be made relatively, physically large to ensure that light from multiple wavelengths would not impinge on the same PMT. Second, the configuration provided little if any flexibility in emission line selection/reconfiguration. Finally, as the number of monitored emission lines increased, so would the corresponding cost (due to the required addition of another PMT). Thus, while the apparatus disclosed in the Joyce patents provided satisfactory performance, it would be desirable to provide an apparatus having a reduced size, weight and cost.
Accordingly, there is a need to provide an improved apparatus for analysis of a fluid sample that minimizes or eliminates one or more of the problems as set forth above.
One object of the present invention is to provide an apparatus for analyzing a fluid sample having a reduced size, weight and cost.
It is a further object to provide such an apparatus configurable for analyzing and characterizing liquid lubricants as well as functional fluids (e.g., hydraulic oils, etc.).
It is yet a further object of the present invention to provide such an apparatus that is highly customizable, and which can be reconfigured to detect and analyze desired, alternate elements.
To achieve these and other objectives, according to one aspect of the present invention, an apparatus for analyzing a fluid sample to determine constituents thereof is provided. The apparatus includes five (5) major parts: a housing, a fluid transfer assembly, an infrared (IR) spectrometer assembly, an optical emission spectrometer (OES) assembly, and a computer controller.
The fluid transfer assembly includes an inlet configured to receive the fluid sample and is configured to selectively flow the fluid sample to an outlet thereof. The IR spectrometer assembly is disposed in the housing, coupled to the outlet, and is configured to analyze the fluid sample and generate a first data set. In a constructed embodiment, the IR spectrometer comprises a Fourier Transform Infrared (FTIR) spectrometer. The OES assembly is also disposed in the housing, coupled to the outlet, and is configured to analyze the fluid sample and generate a second data set. The second data set is substantially continuously valued over a first predetermined wavelength range. Finally, the computer controller is connected to the transfer assembly, the IR spectrometer assembly, and the OES assembly and is configured to control the operation of the apparatus in accordance with a predetermined operating strategy. The computer controller is further configured to determine constituents of the fluid sample in accordance with the first and second data sets.
In a preferred embodiment, the OES assembly includes a fluid sample excitation assembly, such as a spark emission assembly that includes electrodes. The spark assembly is configured to excite the fluid sample to spectroemissive levels to thereby generate radiation characteristic of the constituents in the fluid sample. The OES assembly further includes a first spectrometer configured to receive the radiation and generate a first spectral pattern, and a second spectrometer configured to receive the radiation and generate a second spectral pattern. Also in the preferred embodiment, the first spectrometer has a first resolution, and the second spectrometer has a second resolution less than the first resolution, which preferably may be 0.3 nm (half-width at half-height), and 1.0 nm (half-width at half-height), respectively.
In another aspect of the invention, the IR spectral analyzer assembly is configured to include an inventive flow cell assembly which minimizes the undesirable effects of fringing. xe2x80x9cFringingxe2x80x9d is manifested as a sinusoidal feature in the intensity-versus-wavelength final spectrum, which interferes with the measurement of oil constituents. The IR spectral analyzer assembly includes an IR source, the flow cell assembly, and a detector assembly. The IR source is configured to generate an IR radiation beam focused along a principal axis to converge at the detector. The detector assembly is spaced apart from the IR source. The flow cell assembly includes a sample cell and a compensator window, and is slidably movable along a motion axis transverse to the principal axis. The flow cell assembly moves between a first position wherein the compensator window is optically intermediate the IR source and the detector, and a second position wherein the sample cell is optically intermediate the IR source and the detector.
The compensator window and the sample cell are each arranged such that a respective normal axis associated therewith define a predetermined tilt angle, preferably between about 20-25 degrees relative to the principal axis. Moreover, in a preferred embodiment, the compensator window and the sample cell each have an effective thickness and index of refraction that are substantially equal. The foregoing insures that the focused images of the sample (i.e., through the sample cell), and the background (i.e., through the compensator window) coincide on the detector.
In yet another aspect of the present invention, a method is provided for adjusting the wavelength axis of a sample spectrum of a fluid sample generated by a spectrometer having a pair of electrodes.
The foregoing permits the use of low resolution optical emission spectrometers to identify and quantitate elements, contaminants, and additives of interest in fluid samples.